Perforations provide a mechanism for dividing a web of print media into individually dispensable sheets.
Relevant printing systems dispense individually printed sheets from a continuous web of print media. The individual sheets can be dispensed to recipients by automated cutting or manual tearing of the sheets from the web. However, automated cutting adds mechanical complexity, imposes servicing requirements, and subjects printing systems to mechanical breakdown. Manual tearing shifts some of this burden onto recipients for carrying out the necessary operations. In addition, tearing can produce ragged edges and disturb registration of the print media within the printer.
Perforations have been used to assist tearing along designated lines. However, the amount of force required to tear even perforated lines can vary widely depending upon the direction and position at which the tear forces are applied. Braking mechanisms, which add problems similar to those of automated cutting mechanisms, are sometimes needed to maintain proper registration of the print media within the printers.
So-called xe2x80x9cslitsxe2x80x9d separated by uncut portions referred to as xe2x80x9ctiesxe2x80x9d form the perforated lines, which can extend from one edge to another through a center of the web. Tearing is accomplished most efficiently by applying tensile forces in offset positions that concentrate the tensile forces through one tie at a time. As each tie breaks, the tensile forces shift to the next adjacent tie. Ordinarily, such tearing starts by breaking ties near one edge of the web and proceeds by breaking ties in succession through the center to the other edge of the web.
Other more centered positions for applying tensile forces can distribute the tensile forces through more than one tie at a time. Bursting is accomplished by breaking at least some or all of the ties between both edges of the web at once. The tensile forces required to break all of the ties simultaneously are much higher than those required to break the same ties in succession. Breaking a smaller grouping of the ties simultaneously requires tensile forces intermediate to those required for breaking the ties individually or all at once.
Such wide variability in the tensile forces required to manually separate individual printed sheets along lines of perforation also requires a corresponding capacity for high braking forces and imposes inconsistent demands on recipients to perform the tearing operation. The tensile forces required for bursting all of the ties or even some groupings of the ties can easily exceed reasonable levels for performing manual operations of this sort.
One solution is to weaken the ties to reduce the maximum tensile force required to burst the ties simultaneously. However, the weakened ties also lower the minimum tensile forces required to tear the ties in succession. Such weakened webs are subject to breakage during in-line manufacture, loading into the printer, and subsequent feeding through the printer.
My invention improves the dispensing of perforated sheets from printers and other dispensing devices by reducing variability among tensile forces required to separate the perforated sheets from webs throughout a range of positions at which the tensile forces can be applied. Initiating tearing actions along lines of perforations at one edge or the other of the webs is made relatively more difficult, while initially bursting ties located near the centers of the webs is made relatively easier. For example, perforation patterns can be arranged in accordance with my invention to support a controlled bursting sequence in which ties break in pairs, starting at the web center and proceeding simultaneously toward both edges.
Ordinarily, the minimum tensile forces required to tear lines of perforation are applied from offset positions that initially stress and break the ties located along one of the web edges and proceed by stressing and breaking the remaining ties one at a time. My invention can sustain or even enlarge these minimum tensile forces by maintaining or increasing the strength of ties located near the opposite edges of the webs.
The maximum tensile forces ordinarily required to tear lines of perforation are applied through all of the ties at once. My invention reduces the maximum tensile forces by weakening the ties located at or near the centers of the webs so that these ties break in advance of the rest. Due to the flexible nature of webs, tensile forces applied from the same centered positions stress and break the next adjacent ties paired on opposite sides of the web centers. The remaining ties paired on opposite sides of the web centers are stressed and broken in succession. Thus, even where tensile forces are applied in a manner that initially stresses all of the ties, the ties are still broken in a sequence that greatly reduces the maximum tensile forces.
One example of my new in-line supply of print media is arranged as a web of printable media having regularly spaced lines of perforation that separate the web into individually dispensable sheets. The lines of perforation extend transversely with respect to a longitudinal dimension of the web crossing a longitudinal centerline between two edges of the web. A pattern of ties separated by slits extend along the lines of perforation. The ties occupy a larger portion of the lines of perforation adjacent to the edges of the web than adjacent to the centerline of the web sufficient to relatively increase resistance to tearing near either of the two edges while relatively decreasing resistance to tearing starting near the centerline of the web.
Preferably, the ties located closest to the centerline of the web are weaker than the ties located closest to the edges of the web along the lines of perforation. In addition, the ties are preferably unevenly spaced along the lines of perforation with enlarged spacings separating the ties located closest to the centerline of the web from the remaining ties located closer to the two edges of the web. Once the weaker ties located closest to the centerline of the web have burst, the enlarged spacings encourage the web to pucker, thereby allowing the remaining stronger ties to break in succession from both sides of the web centerline.
The print media itself is preferably made of a flexible non-elastic material. The flexibility permits puckering, while the non-elasticity permits the concentration of tensile forces through limited numbers of ties. Each of the sheets of print media can be individually printed by the printer prior to being dispensed from the printer. One example is a thermal paper having a surface coated with a thermosensitive material that forms images in response to the application of heat in patterns. Tensile forces applied along the centerline of the web between adjacent sheets rupture the ties along the intervening line of perforation in a sequence starting with the ties located closest to the centerline of the web and proceeding in opposite directions through the remaining ties located closer to the two edges of the web. Alternatively, tensile forces applied along either edge of the web can rupture the ties in a more usual sequence starting at one edge and proceeding tie-by-tie to the other edge. However, regardless of where the tensile forces are applied between the edges of the web, comparable tensile forces are required to separate the printed sheets from the web.